Metric time is the measure of time interval using the metric system, which defines the second as the base unit of time, and multiple and submultiple units formed with metric prefixes, such as kiloseconds and milliseconds. It does not define the time of day, as this is defined by various time scales, which may be based upon the metric definition of the second. Other units of time, the minute, hour, and day, are accepted for use with the modern metric system, but are not part of it. The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... Look up second in Wiktionary, the free dictionary. ... An SI prefix (also known as a metric prefix) is a name or associated symbol that precedes a unit of measure (or its symbol) to form a decimal multiple or submultiple. ... A minute is a unit of time equal to 1/60th of an hour and to 60 seconds. ... The hour (symbol: h) is a unit of time. ... Look up day in Wiktionary, the free dictionary. ... Look up si, Si, SI in Wiktionary, the free dictionary. ...

History

When the metric system was introduced in France in 1795, it included units for length, area, dry volume, liquid capacity, weight or mass, and even currency, but not for time. Decimal time of day had been introduced in France two years earlier, but was set aside at the same time the metric system was inaugurated, and did not follow the metric pattern of a base unit and prefixed units. James Clerk Maxwell and Elihu Thomson (through the British Association for the Advancement of Science - BAAS) introduced the Centimetre gram second system of units (cgs) in 1874, in order to derive electric and magnetic metric units, following the recommendation of Carl Friedrich Gauss in 1832. 1795 was a common year starting on Thursday (see link for calendar). ... French decimal clock from the time of the French Revolution Decimal time is the representation of the time of day using units which are decimally related. ... James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and theoretical physicist. ... Elihu Thomson (March 29, 1853 - March 13, 1937) was an engineer who was instrumental in the founding of major electrical companies in the United States, Britain and France. ... The British Association or the British Association for the Advancement of Science or the BA is a learned society with the object of promoting science, directing general attention to scientific matters, and facilitating intercourse between scientific workers. ... This article or section is in need of attention from an expert on the subject. ... Year 1874 (MDCCCLXXIV) was a common year starting on Thursday (link with display the full calendar) of the Gregorian calendar (or a common year starting on Saturday of the 12-day slower Julian calendar). ... Johann Carl Friedrich Gauss or Gauß ( ; Latin: ) (30 April 1777 – 23 February 1855) was a German mathematician and scientist who contributed significantly to many fields, including number theory, analysis, differential geometry, geodesy, electrostatics, astronomy, and optics. ... Year 1832 (MDCCCXXXII) was a leap year starting on Sunday (link will display the full calendar) of the Gregorian Calendar (or a leap year starting on Friday of the 12-day slower Julian calendar). ...

The ephemeris second (defined as 1/86400 of a mean solar day) was made one of the original base units of the modern metric system, or International System of Units (SI), at the 10th General Conference on Weights and Measures (CGPM) in 1954. The SI second was later redefined more precisely as: the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. Look up si, Si, SI in Wiktionary, the free dictionary. ... The General Conference on Weights and Measures is the English name of the Conférence générale des poids et mesures (CGPM, sometimes written in English Conférence Générale des Poids et Mesures). ... Year 1954 (MCMLIV) was a common year (link will display full calendar) of the Gregorian calendar. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ...

Alternative units

Numerous proposals have been made for alternative base units of metric time. On March 28, 1794, the president of the commission which developed the metric system, Joseph Louis Lagrange, proposed in a report to the commission the names déci-jour and centi-jour (deciday and centiday in English).^[1] Base units equivalent to decimal divisions of the day, such as 1/10, 1/100, 1/1000, or 1/100,000 day, or other divisions of the day, such as 1/20 or 1/40 day, have also been proposed, with names such as tick, meck, chi, chron, moment, etc., and multiple and submultiple units formed with metric prefixes. Such alternative units have not gained any notable acceptance, however, mostly from sheer lack of acquaintance and familiarity. is the 87th day of the year (88th in leap years) in the Gregorian calendar. ... 1794 was a common year starting on Wednesday (see link for calendar). ... The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... Joseph-Louis Lagrange, comte de lEmpire (January 25, 1736 – April 10, 1813; b. ... deci- (symbol d) is a prefix in the SI system of units denoting a factor of 10−1 (1/10). ... Centi (symbol c) is a SI prefix in the SI system of units denoting a factor of 10-2, or 1/100. ...

A modified second = 1/100 000 of a day = 0.864 s could be a viable alternative. Any redefinition of the second, however, creates conflicts with anything based on its precise current definition. Another unit for time, more familiar than some other suggestions, could be 14.4 minutes, i.e. a shorter quarter of an hour, or a centiday, as proposed by Lagrange. The centiday was used in China (called ke in Chinese) for thousands of years, until the Jesuits had it redefined from 1/100th of a day to 1/96th of a day (i.e., 15 minutes) in the 17th century. Ke (刻) is a traditional decimal time unit equalling 14. ... The Society of Jesus (Latin: Societas Iesu), commonly known as the Jesuits, is a Roman Catholic religious order. ... (16th century - 17th century - 18th century - more centuries) As a means of recording the passage of time, the 17th century was that century which lasted from 1601-1700. ...

In the 19th century M.J. de Rey-Pailhade proposed using the centiday, abbreviated cé, divided into 10 decicés, 100 centicés and 1000 dimicés.^[2] Alternative meaning: Nineteenth Century (periodical) (18th century — 19th century — 20th century — more centuries) As a means of recording the passage of time, the 19th century was that century which lasted from 1801-1900 in the sense of the Gregorian calendar. ...

In 1897, the Commission de décimalisation du temps was created by the French Bureau of Longitude, with the mathematician Henri Poincaré as secretary. The commission proposed making the standard hour the base unit of metric time, but the proposal did not gain acceptance and was eventually abandoned.^[3] The Bureau des Longitudes is a French scientific institution, founded by decree of June 25, 1795 and charged with the improvement of nautical navigation, standardisation of time-keeping, geodesy and astronomical observation. ... Jules TuPac Henri Poincaré (April 29, 1854 – July 17, 1912) (IPA: [][1]) was one of Frances greatest mathematicians and theoretical physicists, and a philosopher of science. ... The hour (symbol: h) is a unit of time. ...

Alternative meaning

Metric time is sometimes used to mean decimal time. Metric time properly refers to measurement of time interval, while decimal time refers to the time of day. Standard time of day is defined by various time scales, such as UTC, which are now usually based upon the metric base unit of time, the second. Some proposals for alternative units of metric time are accompanied by decimal time scales for telling the time of day based upon these alternative units. Other proposals called "metric time" refer only to decimal time, and therefore are not truly metric. French decimal clock from the time of the French Revolution Decimal time is the representation of the time of day using units which are decimally related. ... ...

French decimal time is sometimes called "metric time" because it was introduced around the same time as the metric system and both were decimal, but it was not part of the decree creating the original metric system and its units were named for the hour, minute and second, instead of using metric prefixes. Other decimal time standards, such as Swatch Internet Time, are not considered metric time. The hour (symbol: h) is a unit of time. ... A minute is a unit of time equal to 1/60th of an hour and to 60 seconds. ... Look up second in Wiktionary, the free dictionary. ... Swatch Internet Time is a concept introduced in 1998 and marketed by the Swatch corporation as an alternative, decimal measure of time. ...

In computing

In computing, at least internally, metric time gained widespread use for ease of computation. Unix time gives date and time almost as number of seconds since January 1, 1970, and Microsoft's FILETIME almost as multiples of 100ns since January 1, 1601 ^[4]. VAX/VMS uses the number of 100ns since November 17, 1858. (Each of these is not strictly linear, as they have discontinuities at leap seconds.) Unix time, or POSIX time, is a system for describing points in time: it is the number of seconds elapsed since midnight UTC on the morning of January 1, 1970, not counting leap seconds. ... is the 1st day of the year in the Gregorian calendar. ... 1970 (MCMLXX) was a common year starting on Thursday. ... is the 1st day of the year in the Gregorian calendar. ... Events February 8 - Robert Devereux, 2nd Earl of Essex, rebels against Elizabeth I of England - revolt is quickly crushed February 25 - Robert Devereux beheaded Jesuit Matteo Ricci arrives in China Bad harvest in Russia due to rainy summer Dutch troops drive Portuguese from Málaga Battle of Kinsale, Ireland Births... OpenVMS[1] (Open Virtual Memory System or just VMS) is the name of a high-end computer server operating system that runs on the VAX[2] and Alpha[3] family of computers developed by Digital Equipment Corporation of Maynard, Massachusetts (DIGITAL was then purchased by Compaq, and is now owned... 17 November is also the name of a Marxist group in Greece, coinciding with the anniversary of the Athens Polytechnic uprising. ... 1858 (MDCCCLVIII) is a common year starting on Friday of the Gregorian calendar (or a common year starting on Sunday of the 12-day-slower Julian calendar). ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ...

In popular culture

In the science fiction novel A Deepness in the Sky, the spacefaring Qeng Ho culture is depicted as using metric units such as the kilosecond and megasecond for all time interval measurements. In fact, as the culture has no tie to any planet, this is the only timekeeping system depicted; it has no concept of day or of time of day. Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ... In 1999 Vernor Vinge published his science fiction novel, A Deepness in the Sky, a loose prequel (set 30,000 years earlier) to his novel A Fire Upon the Deep (1992). ...

References

1. ^ Procès-verbaux du Comité d'instruction publique de la Convention nationale by James Guillaume
2. ^ Report of the Sixth International Geographical Congress: Held in London, 1895
3. ^ Einstein's Clocks, Poincare's Maps: empires of time By Peter Louis Galison
4. ^ FILETIME documentation on MSDN

External links

• Metric unit of time (second) Official text of SI brochure from International Bureau of Weights and Measures
• Metric Time? University of Illinois Physics Department
• Decimal Time - Metric Time explains the difference between decimal time and metric time